This relates to imaging systems and, more particularly, to image sensing pixels with feedback loops.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) may be formed from a two-dimensional array of image sensing pixels. Each pixel receives incident photons (light) and converts the photons into electrical signals. Image sensors are sometimes designed to provide images to electronic devices using a Joint Photographic Experts Group (JPEG) format.
Typical imaging sensing pixels include a photodiode that receives incident light and converts the light into an electrical charge, a floating diffusion node, a transfer transistor that shifts the electrical charge to the floating diffusion node, and an output amplifier with an input connected to the floating diffusion node. The performance of conventional imaging sensing pixels is, however, limited by the transfer efficiency and speed of the transfer transistor in each pixel (e.g., the efficiency of the transfer transistor in transferring all of the charge from the photodiode to the floating diffusion node and the speed at which the charge is transferred).
It would therefore be desirable to provide image sensing pixels with feedback loops for imaging systems.